Power Button don't work

I have a Laptop Inspiron 5558 and recently I have a hard Time to turn the Compurter on.

I have to press the Power Button and hold it down for a few minutes before the Computer launch into Windows. I checked the Battery and the Power Cord , that is working and I face no other issue with my Laptop.Soon my Laptop is on is running fine

What shal I do?

thanks in Advance